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Into the Soil

The Bartlett Tree Research Lab in Charlotte studies how best to protect trees and tree root systems in a rapidly growing state where building is happening everywhere.

CHARLOTTE AREA — Who doesn’t love trees?

They provide shade, they produce the oxygen we breathe and they add beauty to any landscape—if the leaves change colors in the fall they become even more beautiful. Yes, it’s difficult not to love a tree.

And when you walk around the Arboretum at the Bartlett Tree Research Lab near Charlotte with Kelby Fite, you find yourself loving trees even more. Fite is the director of the 400-acre facility.

Not only is the facility beautifully landscaped with trees dotting sloping hillsides and lining the shores of lakes, but it is also carefully planned. Elm trees are planted in one corner of the facility, while maples, oaks, magnolias and all types of conifers grow in other areas. There is even a section containing trees that are transplanted from other areas.

The arboretum provides researchers with an opportunity to study trees in an urban environment.

“A forest environment in a native ecosystem is much different from what most urban and suburban landscapes are like,” explains Fite. “So the stresses that plants endure in the urban and suburban environment are completely different from a natural forest. So we have to design management plans that are different for those trees compared to that of a native forest.”

Those stresses include coping with development. For example, take the case of a homeowner who wants to build a driveway or add a drainage line on to their house. The project would be much easier if the homeowner could figure out where the roots are that belong to the large tree near the project site.

“Right now, the only way to find the roots is to start digging,” says Daniel Markewitz, Ph.D., and professor of forest soils at the University of Georgia. “If there was a way to find the roots in advance, you could better protect the beautiful tree during the remodeling project.”

Trees absorb water and nutrients through their roots. Those roots also anchor the tree to the ground. Arborists, the scientists who study trees, say roots generally extend as far out from the tree trunk as the drip line—that’s where the water falls off of the tree canopy. Roots can also sink three to four feet deep.

Scientists also say up to 20-percent of a tree’s roots can be destroyed without killing the tree. It turns out that trees are pretty resilient.

But in its quest to find water, a tree will send its roots growing much farther and much deeper than expected. That means roots aren’t always where you think they are.

And for trees in an urban environment, that’s a problem.

“We tend to have this vision that the tree grows roots everywhere in this nice, bulbous pattern because we look at branches that way,” explains Markewitz, as he cups his hands to form a rounded ball shape.

“But look up at this tree,” he says gesturing to the canopy of branches above his head. “There are no constraints up here, I grow where I want to grow and if there is a rock ledge near one side of the tree, the roots will go down and around. Or they just won’t grow there and they will grow farther out on another side.”

The bottom line is that while a contractor may think they're only take out 20-percent of the roots on one side, without knowing where the rest of the root system is that may be a majority of the tree’s root system.

So scientists are using the arboretum’s trees to study multiple ways to locate tree roots without digging them up in order to find them.

The portable electromagnetic induction unit sends electromagnetic waves into the soil by means of a portable rod, which is carried across the ground in a grid pattern. Sensors pick up how the waves are being reflected off of objects underground. A GPS unit records those locations.

At a present set-up at the arboretum, near the induction unit, a maze of wires connected to a computer and a battery surround another tree. This system measures soil electrical resistivity. The computer sends out electrical currents through the wires and the current is fired into the ground through metal spikes that are spread throughout the wire maze.

“And the system moves the injection point around the grid, and we’ll be able to create a 3D image of below ground,” explains Markewitz, pointing from one spike to another. “It has a program to change the injection point and the measurements point from there, to there and to over there. And as we get the readings of the different amounts of resistance, we work backwards and create an image of what the below ground environment is like.”

Neither system creates a perfect picture of what is underground, but it appears they both could provide a good indication of where a root system might be.

“A tree is only as healthy as its roots system," says John Ashley Reese, a graduate student in natural resources at the University of Georgia who is helping with the tree root project. “You can say you have nice healthy soil, drainage and a perfect location for a tree, but if you don’t know where the roots are you could be in trouble. In the urban environment, knowing where the roots are is pretty important."